1. Field of the Invention
The present invention is directed to the field of liquid level sensing and more particularly to the area of electrically conducting liquid level sensors for use on radiators of liquid cooled engines.
2. Description of the Prior Art
The sensing of the liquid coolant level in a radiator of an associated engine is especially important to the owner of such an engine, since it provides another means for preventing severe damage to the engine. Sensors which measure engine temperature, oil pressure and oil level are well known and, when connected to appropriate warning circuitry, provide essential monitoring features. Monitoring of the level of coolant in a radiator is also important since a reduction of coolant volume will affect the cooling efficiency of the cooling system and in turn affect the operation of the engine. In severe cases where the coolant is lost, due to a leak in the radiator or associated connecting lines, the engine could be severely damaged if a reliable coolant level monitoring system is not in use.
A low coolant sensor is disclosed in U.S. Pat. No. 3,845,464 as mounted within a cavity adjacent to the water passages of an engine. The sensor includes a variable resistance element that is connected to the battery of the associated vehicle and is heated by the electrical current flowing through the element to ground. When the resistance element is in contact with the coolant liquid, it is at a lower temperature due to the cooling effect of the coolant liquid and exhibits a higher resistance state than when it is not in contact with the coolant liquid and reaches a higher temperature. The lowering in resistance, due to a coolant level that is below the sensor, is detected by a simple series circuit in which a lamp is illuminated by the increased current flow.
A liquid level sensor is shown in U.S. Pat. No. 4,277,773 as configured and connected to provide an electrical current through the liquid in contact with its sensor elements to the grounded radiator. Such current flow completes a series circuit by which an indicator lamp is energized whenever the coolant level is high enough to provide a significant current flow between the sensor elements and ground.
It is apparent that in each of the prior art references noted above, the intensity of the warning lamp is dependent upon the amount of current flowing through the sensor to ground and will be effected by sloshing and splashing of the coolant about the sensor.